Humans and other animals are a rich source of mechanical power. In general, this mechanical power is derived from chemical energy. The chemical energy required for a muscle or group of muscles to perform a given activity may be referred to as the “metabolic cost” of the activity. In humans and other animals, chemical energy is derived from food. Food is generally a plentiful resource and has a relatively high energy content. Humans and other animals exhibit a relatively high efficiency when converting food into chemical energy which then becomes available to muscles for subsequent conversion into mechanical energy. Mechanical power generated by humans and other animals can be efficient, portable and environmentally friendly.
As a consequence of the attractive characteristics of human power, there have been a wide variety of efforts to convert human mechanical power into electrical power, including:                U.S. Pat. No. 1,472,335 (Luzy);        U.S. Pat. No. 1,184,056 (Van Deventer);        U.S. Pat. No. 5,917,310 (Baylis);        U.S. Pat. No. 5,982,577 (Brown);        U.S. Pat. No. 6,133,642 (Hutchinson);        U.S. Pat. No. 6,291,900 (Tiemann et al.).        
A subset of the devices used to convert human mechanical power into electrical power focuses on energy harvesting—the capture of energy from the human body during everyday activities. Examples of disclosures relating to energy harvesting include:                Starner, T., Human-powered wearable computing. IBM Systems Journal, 1996. 35(3-4): 618-629;        Chapuis, A. and E. Jaquet, The History of the Self-Winding Watch. 1956, Geneva: Roto-Sadag S.A.;        Shenck, N. S. and J. A. Paradiso, Energy scavenging with shoe-mounted piezoelectrics. IEEE Micro, 2001. 21(3): 30-42;        Kymissis, J., et al. Parasitic Power Harvesting in Shoes. in Second IEEE International Conference on Wearable Computing. 1998: IEEE Computer Society Press;        Antaki, J. F., et al., A gait-powered autologous battery charging system for artificial organs. Asaio J, 1995. 41(3): M588-95;        Gonzalez, J. L., A. Rubio, and F. Moll. A prospect on the use of piezolelectric effect to supply power to wearable electronic devices. in ICMR. 2001. Akita, Japan;        Moll, F. and A. Rubio. An approach to the analysis of wearable body-powered systems. in MIXDES. 2000. Gdynia, Poland;        Drake, J., The greatest shoe on earth, in Wired. 2001. p. 90-100;        Niu, P., et al. Evaluation of Motions and Actuation Methods for Biomechanical Energy Harvesting. in 35th Annual IEEE Power Electronics Specialists Conference. 2004. Aachen, Germany: IEEE.        U.S. Pat. No. 6,768,246 (Pelrine et al.);        US patent publication No. US2004/0183306 (Rome);        U.S. Pat. No. 6,293,771 (Haney et al.).        
For a variety of reasons, the energy harvesting apparatus disclosed by these authors have experienced limited power generation capacity and/or limited commercial viability or success. Drawbacks of the prior art energy harvesting apparatus contemplated in these disclosures include: lack of implementation detail; low power yield; and heavy and/or awkward energy harvesting apparatus, which can lead to relatively high metabolic energy costs and correspondingly low energy conversion efficiency and/or impairment of normal physical activity, for example.
There is a desire to provide improved methods and apparatus for harvesting biomechanical energy.